The present invention is directed to structural members for vehicles, including motor driven vehicles and trailers. In particular, it is directed to frame members for such vehicles, including boat trailers. Vehicle construction, including the design of frames and structural members for frames and sub-frames has evolved with improvements in the metallurgy of the materials which have also opened advances in manufacturing processes.
With the advent to high-strength, corrosion-resistant, aluminum alloys, structural members previously made from rolled steel have steadily given way to extruded aluminum alloy members. With these aluminum structural members being suitable for extrusion manufacture, not only has the weight of a vehicle been reduced, but the extrusion manufacturing has opened paths for making structural member shapes not previously practical in rolled members or cast members. Extrusion manufacturing has also eliminated stamping steps often used in steel member manufacturing.
Boat trailers, being on-the-road vehicles, are subject to DOT (U.S. Department of Transportation) regulations for strength, durability, and safety. Side rails and cross members, being the primary structural support members of a boat trailer frame, are subject to DOT standards as a part of certifying the entire trailer. The side rails and cross members form the frame (or skeleton) of a trailer to support the boat cradle members, to carry the hitch coupling, and to be connected to the wheel axel(s). A boat trailer frame is subject to many types of forces, from bending to torsion to compression to tensile forces. Not only must each member be strong enough to withstand these forces, but the couplings between members must also.
Painted steel tubing was used for many years for boat trailer side rails and cross members. To ward off corrosion and to enhance appearance, galvanized steel tubing steadily began to replace painted steel. However, zinc coatings can crack, are affected at weld points, and discolor with use. High strength, corrosion-resistant aluminum alloys have begun to be used for boat trailer structural members, including cross members and side rails. These aluminum structural members are more attractive than galvanized members at the off-set, and maintain their appearance longer. Extruded tubes, either C-channels or box-tubes, were first used. Recently an aluminum I-beam has been used for boat trailer side rails by Load Rite Trailers, Inc. of Fairless Hills, Pa.
The assembly of aluminum structural frame members on boat trailers has followed the assembly practices with painted steel and galvanized steel members. Namely, they were drilled through for bolts, punched for fasteners, welded, or clamped together with U-bolts. Not only are these assembly practices relatively labor intensive and therefore relatively expensive, the hardware use is costly. Moreover, once drilled or stamped or welded, the assembly positions became fixed and later adjustments are precluded. While U-bolts and clamps are adjustable, they are generally unsightly, and can work loose especially if struck being a catch point.
While an I-beam shape provides strength and rigidity, its cross-sectional configuration is awkward for attaching fenders, axels, load bearing cross bars, tie-down brackets, and the like, without through drilling the web or the top or bottom flanges and through bolting. Alternatively welding or clamping can be used. Such through drilling and bolting or such welding and heat treating adds to the cost of manufacturing and may weaken the beam or set up undesirable stress points (stress risers). U-clamping has the same short comings as with other structural members of other cross-sectional shapes.
What is desired is a structural member for a vehicle, including a C-channel, a tube, and an I-beam, which carries a slot in one wall, for holding a bolt or bolts, for joining thereto another structural member, or another component of the vehicle.
What is secondly desired is that such a slot hold the head of each bolt with the threads extending outwardly and also hold each bolt in position once the bolt is tightened with its mating nut, whereof such slot also holds the bolt from turning while the tightening process is carried out.
What is further desired is that such slot be capable of withstanding the forces applied to the structural member without a tear out of the bolt head.
What is even further desired is that such slot permits the structural member to be bolted to such trailer members as fenders, axels, load bearing cross bars, tie down brackets and the like.
Placing a slot in a structural member such as an I-beam, for holding a bolt or an anchor member is not new. These prior art slotted beams have been designed as building structural members and not for use in vehicles. Their designs depart from the scope and direction of the present invention.
Timm, U.S. Pat. No. 1,561,126, shows a channel for receiving and holding the square head of a stove bolt. Phillips, U.S. Pat. No. 2,909,054, shows a metal box with a slot for holding a concrete anchor. Burrell, U.S. Pat. No. 4,159,604, shows an aluminum joist with a slot for receiving and holding the hex-head of a machine bolt. Stanford, U.S. Pat. No. 4,584,809, shows a fabricated wood-metal composite I-beam with an extruded aluminum bottom flange, which has a T-shaped slot for receiving the head of a bolt. Janson, U.S. Pat. No. 4,285,095 shows a cruciform-shaped slot in a crane beam for receiving and holding a variety of members from a bolt to a trolley wheel. Marsland, U.S. Publication No. 2005/0284078 A1, shows an I-beam used as a structural joist having a slot in the bottom flange including notches for receiving the flange portion of the head of a bolt.
The Janson slot is large enough to accommodate a wrench placed on the head of a bolt when tightening the bolt, Phillips requires a clip to hold his anchor from turning.
Germane to the design of each prior art slot is the fact that each slot cavity has rectangular walls. This means that the walls transition at right angles Any lateral force exerted against a wall of these slots remains a strict bending moment (bending force). A tightened bolt has its head exert a permanent preloaded stress point in the weakest direction of the slot wall.
Timm, Burrell, Stanford and Marsland each require the shape of their slots, i.e., the walls of a respective slot, to hold their respective bolt heads from turning. Thus the sidewalls of these slots have corners of the bolt head providing a force pressing against the sidewalls as the bolt is tightened against them. When the bolt is fully tightened, there is a “preloaded” stress riser created by the abutment of the bolt head corners, which remains at that location of a respective sidewall.
If the tightening torque exceeds the strength of the sidewalls, the Timm, Burrell, Stanford and Marsland bolt heads can spin. If the forces imparted to these bolts create a further torque a sidewall could fail at a preloaded stress riser permitting the bolt to rotate.
The shape of the slots and the shape of the I-beam flanges in the above prior art are adequate for the static loading found in residential or commercial construction. However, they are undesirable for the dynamic loading, including the torque and bending moments, experienced by vehicle structural members, including frames and sub-frames, and also experienced by trailer side rails.